1. Field of the Invention
The described invention relates generally to the field of subscription services such as, for example, presence services, and particularly, but not exclusively, to the support of subscription services using session initiation protocol dialogs.
2. Description of the Related Art
Typically, in 3GPP all-IP architectures, users may subscribe to subscription services. The subscription service is usually initiated using subscription messages. The preferred subscription messages often utilise SIP (Session Initiation Protocol) messages. On detection of a subscribed event, a subscription server normally notifies the subscriber of the event, commonly using notification messages. In known systems, the subscription and/or the notification messages are generally facilitated by a proxy server configured as a connection processing server (CPS). The subscription typically establishes an SIP dialog through the CPS, and the CPS usually maintains that dialog and it is normally used for all notifications. In this way the CPS normally effectively records the route of the subscription.
In many practical implementations, a CPS may support a large amount of subscriptions, and the common necessity to record a large number of routes associated with a large number of subscriptions in order to facilitate notifications may significantly impinge upon the resources of the CPS. In addition, for a large amount of time the dialogs associated with the recorded routes and stored in the CPS are generally unused. Therefore the capacity of the CPS is typically used by inactive dialogs.
3GPP IMS Release 6 introduces the presence service. 3GPP TS 23.241 6.1.0 defines that a presentity's serving call state or session control function (S-CSCF) is at least usually not required to record-route the dialog of the subscription for the presence service. ‘Record-routing’ of the subscription normally effectively involves the S-CSCF, acting as a proxy server for the dialog, recording the route of the subscription messages. More particularly, it commonly involves the proxy server storing the dialog details, in other words, maintaining the dialog once the subscription is set up. The usual disadvantage with the proxy server maintaining the ‘record-route’ is that it typically utilises the limited resources of the proxy server.
A problem generally exists in providing a proxy server with the ability to know when it is appropriate not to record the route and when recording of the route would be advantageous, depending on the type of services being accessed.
It is therefore an aim of certain embodiments of the present invention to address one or more of the above-stated problems.